One known method for abating certain diesel engine exhaust constituents is by use of an exhaust after-treatment system that utilizes Selective Catalytic Reduction (SCR) of nitrogen oxides. In a typical SCR system, urea or a urea-based water solution is mixed with exhaust gas. In some applications, a urea solution is injected directly into an exhaust passage through a specialized injector device. The injected urea solution mixes with exhaust gas and breaks down to provide ammonia (NH3) in the exhaust gas stream. The ammonia then reacts with nitrogen oxides (NOx) in the exhaust at a catalyst to provide nitrogen gas (N2) and water (H2O).
As can be appreciated, exhaust after-treatment systems that utilize SCR require the presence of some form of urea close to the engine exhaust after-treatment system such that the urea can be continuously supplied during operation. Various urea or urea-solution delivery systems are known and used in engine applications. In known urea injection systems, a buildup of injected urea can occur when urea becomes deposited on surfaces of the SCR system. The urea buildup, which may involve crystallization of the deposits, can adversely affect flow-through of exhaust gases through the system and reduce the efficiency of the reaction of the urea with the nitrogen oxides. In addition, it has been recognized that buildup and fouling of the injector tip itself will adversely affect the urea solution spray pattern and penetration generated by the injector. Therefore, buildup of urea on various components is of concern.
It will be appreciated that this background description has been created by the inventors to aid the reader, and is not to be taken as an indication that any of the indicated problems were themselves appreciated in the art. While the described principles can, in some respects and embodiments, alleviate the problems inherent in other systems, it will be appreciated that the scope of the protected innovation is defined by the attached claims, and not by the ability of any disclosed feature to solve any specific problem noted herein.